1. Technical Field
The present invention relates to a system and method for setting a RW (read/write) offset in a hard disk device (HDD) to cancel the offset between the read and write heads of the disk device. This disk device includes a rotary actuator where both the write and read heads access a sector-servo type disk recording medium. The present invention also includes a system and method for recovering a read data error of data recorded in a disk device accessing a disk recording medium with a head section implemented in a rotary actuator.
2. Description of the Related Art
A hard disk device (HDD) (including a sector-servo type disk D) surface, as shown in FIG. 2, is divided into data areas DF and servo areas SF. A combination type head section H (see FIGS. 1 and 4) that includes a write head Hw for writing user data on the disk D, a read head Hr for reading data, and a rotary actuator 2 (see FIG. 1) for moving the head section H along in a radial direction of the disk D is also included in HDD. A RW offset xcex94W, as shown in FIG. 4, is the offset amount of read head Hr from the reference position at the time of data writing.
A control unit of the disk device recognizes only a position of read head Hr on the basis of a read signal of servo information area by read head Hr. It is necessary to require write head Hw to track a desired position while compensating for the RW offset when user data is recorded by write head Hw. Read head Hr must also track a desired position while shifted by the RW offset when user data is read by read head Hr. It is necessary to set the RW offset in the disk device before disk operation. Additionally, the dimensions and positional relations of write head Hw and read head Hr differ with every head section H and it becomes necessary to calculate the RW offset for every head section H.
As shown in FIG. 4, a yaw angle xcfx86 between the longitudinal direction (disk-circumferential direction) of a track and head section H changes depending on a position of the track (radius from a disk center). The RW offset has a different value for every track. The RW offset must be set for every track in the disk device before disk operation.
Furthermore, since the RW offset varies for every disk device and for every head section H, the RW offset is set in the disk device by individually finding the RW offset by measuring and calculating a value from a test.
In the following description, the tracking position is a position in a radial direction (the direction of track width) of the disk where write head Hw or read head Hr is positioned. Additionally, an on-track position is a target position where data is recorded by write head Hw. The on-track position is also the target tracking position of the read head Hr when the data is read from the disk. Furthermore, an off-track position is every tracking position that is not an on-track position.
The write offset is an offset amount of read head Hr from a reference position (for example, a center of track width) when the data is read from the disk. The RW offset is the shift amount between write head Hw and read head Hr in a radial direction. If the write offset is zero, the offset amount of read head Hr from a reference position when the data is read, and the shift amount between write head Hw and read head Hr become equal. In addition, if the write offset is not zero, the offset amount of read head Hr from the reference position at the time of data reproduction has a value found by adding the write offset to the shift amount between write head Hw and read head Hr. In the RW offset, the shift amount between write head Hw and read head Hr is the critical value. Therefore, it is assumed that the RW offset refers to the shift amount between write head Hw and read head Hr in a radial direction of a disk.
For example, in FIG. 5, a reference position of a track T(j) is a position of r=r(j), and since, at the time of data recording as shown in FIG. 5A, read head Hr tracks to the reference position, the write offset is 0. In FIG. 5A, data is recorded by write head Hw at the on-track position which separates write head Hw and read head Hr from the reference position by the shift amount xcex94W (=RW offset). During a data read, read head Hr tracks to a position separating from the reference position by the RW offset xcex94W. If the write offset is not zero, read head Hr tracks to a position found by adding the write offset to the shift amount xcex94W between write head Hw and read head Hr.
It is well-known in the art that the MSE (Mean Square Error) method is utilized for setting the RW offset in a disk device. The MSE method includes the steps of:
writing a predetermined test pattern in each data area within tracks selected to be measured;
finding a corresponding value of difference between real read signals and ideal response signals of the test patterns at a plurality of different tracking positions;
searching a tracking position where the MSE value minimizes; and
finding a RW offset for the track to be measured, on the basis of this tracking position where the MSE value is minimal.
Furthermore, as described above, the RW offsets of the plurality of tracks to be measured are found by an interpolation of these RW offsets of the tracks to be measured and are set in the disk device.
If a recording position is unintentionally shifted, user data is recorded at a position that is shifted from an on-track position for a data sector. In this case, if a set RW offset is used, a read data error may occur since the data recorded in the data sector cannot be read correctly. In a disk device, if an error occurs at the time of read operation, a error recovery procedure is executed about the data sector where the read data error occurs. The error recovery procedure (ERP) includes the steps of retrying the data read at the same position where the error occurred or by shifting the disk slightly to attempt to find the requested data in adjacent tracks.
However, setting a RW offset by the MSE method, a skill well-known in the art, the data area used for a test pattern is usually limited to a few data sectors. It is not possible to measure all points in a data track area. Because of this, the precision of the MSE values is poor, and frequently, the error due to this imprecise value is included in a set RW offset. Therefore, it is necessary to increase the number of data sectors and tracks that are measured in order to increase the precision of RW offsets. This, however, increases the time latency for RW offset calculations. Also, if the number of data sectors and the number of tracks measured are increased, the precision of the MSE values becomes especially degraded when a GMR head is used for a read head or when there is an extremely fine track pitch.
Additionally, in a method well-known in the art of setting a RW offset on the basis of a tracking position where a level of a read back signal maximizes, precision is insufficient only when means for approximately finding the RW offset is simply given as a maximum.
As described above, if the RW offsets in a disk device include measurement errors, the disk device cannot continue to read data at optimum positions, and errors may frequently occur at the time of read operation.
In the error recovery procedure (ERP), an error recovery may require a large time latency, because it is not feasible to find a lost track smoothly if the recording position is shifted unintentionally.
The present invention solves such conventional problems, and its object is to reduce the occurrence of read data errors by enhancing the setting precision of RW offsets. In addition, another object of the present invention is to reduce time latency required for error recovery handling.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.
The RW offset setting method of the present invention includes the steps of:
[A] recording a test pattern by a write head in each of a plurality of tracks to be measured, which are selected from among the tracks in the disk recording medium;
[B] reading the test pattern by a read head at each of a plurality of different tracking positions for each of the plurality of tracks to be measured, and measuring an amplitude of a read back signal at each tracking position;
[C] finding an approximate expression of a profile of the measured amplitude for the plurality of tracking positions about each of the plurality of tracks to be measured;
[D] finding a position, which gives a maximum value in the approximate expression, about each of the plurality of tracks to be measured as a tracking position where amplitude of the read back signal maximizes, and finding a RW offset based on this tracking position; and
[E] setting a RW offset for all tracks in the disk device based on the RW offsets about the plurality of tracks to be measured.
In step [A], the tracks to be measured are selected among different track areas (for example, an area in an inner diameter side, an area in an outer diameter side, and an intermediate area). One track can be designated as the representative track measured in the area, or a plurality of tracks adjacent to each other can be measured to get a more accurate reading. If a plurality of adjacent tracks are measured, two or four adjacent tracks consisting of a period of a repeated wedge burst pattern of servo information are usually selected. The amplitude of the read back signal is measured for each track adjacent to another at the step [B], and the mean of the amplitude or position in the respective adjacent tracks is calculated. This mean is the representative value of the area. This mean is calculated to reduce the measurement error that might be obtained (for example, a write position shift at the time of servo write) and an error caused by inequality of a pattern by measuring a plurality of tracks adjacent to each other in this manner. A RW offset is calculated from the mean.
It is possible to increase the precision of the calculation by measuring the amplitude of signals in a whole track or as many data sectors as possible. Therefore, it is desirable to record test patterns over the perimeter.
Furthermore, without simply making a RW offset be a tracking position where the maximum amplitude is measured, the RW offset is made at a position where a maximum value of an approximate expression of an amplitude profile exists. It should be readily apparent to those skilled in the art that this maximum value can be found by taking a limit or by taking a derivative of the approximate expression. By calculating the percent difference between the two methods, it is possible to negate the effects of unimportant data. Usually, a quadratic equation is used for the approximate expression.
A RW offset for any track is usually given in a multiple-degree equation, with an input value as a track identification number. For example, if a cubic equation is used, there are four coefficients, and hence, values measured at a minimum of four positions are necessary. Alternatively, the four coefficients can be found with the least squares method, a skill well-known in the art, while increasing the number of measurement positions to five or six. Alternatively, it may not be necessary to find all the coefficients. For example, in a cubic equation, only the zero-degree and linear coefficients are found from values at two positions. The quadratic and cubic coefficients are not changed from predetermined values. With this method, sufficient precision may be obtained. Also, this method makes it possible to shorten the test time. Treatment of failed measurements becomes simple because the probability of measurement failure increases when there are a greater number of coefficients to be found.
The present invention also includes a method for recovering a read data error of recorded data in a disk device with a rotary actuator having a head section for accessing a disk recording medium, which includes the following steps:
[A] determining an off-track direction, where the amplitude increases, by having the head section perform tracking at off-track positions in both sides of an on-track position and measuring the respective amplitude of read back signals by the head section in the vicinity of a data sector where a read data error occurs;
[B] searching an off-track position where the amplitude becomes a local maximum by gradually shifting the head section in the off-track direction where the amplitude increases and measuring the amplitude at each off-track position; and
[C] reading data recorded in the data sector having the head section track to the off-track position where the amplitude becomes a local maximum.
In another preferred embodiment of the present invention, a read data error recovery method including:
[A] tracking to a plurality of different tracking positions with the head section within a predetermined range in regard to a track where the read data error occurs and measuring each amplitude of read back signals by the head section in the vicinity of a data sector where a read data error occurs;
[B] finding an approximate expression of a profile of the measured amplitude for the plurality of tracking positions and designating a position where a maximum value is given in this approximate expression as a tracking position where amplitude of the read back signal maximizes; and
[C] reading data recorded in the data sector by tracking with the head section to the off-track position where the amplitude maximizes.
In the both the RW offset setting and read data error recovering methods in a preferred embodiment of the present invention, there is a method for reading an amplification degree in an AGC (Automatic Gain Control) circuit before digital sampling. In any method, it is possible to measure the amplitude quickly without an amplitude measurement instrument outside of an HDD. When the amplification degree in an AGC circuit is large, the amplitude of an input signal is small.
The methods for reading an amplification degree can be executed at high speeds. The methods are suitable for finely measuring:
a profile of amplitude of read back signals;
a amplitude at several measurement positions in one track to find their mean; and
each amplitude about a plurality of tracks that are adjacent to each other and averaging the calculations to find the mean.
Therefore, it is possible to improve measurement precision. Furthermore, the methods for reading an amplification degree have excellent data repeatability, and hence it is possible to smoothly search for a lost data written track in error recovery when a write position is unintentionally shifted.
Next, a disk device of a preferred embodiment of the present invention, includes:
a sector-servo type disk recording medium where servo information is recorded in a servo area;
a head section including a write head and a read head for accessing the disk recording medium;
a rotary actuator for retaining and moving the head section along in a radial direction of the disk recording medium; and
a control means for controlling the rotary actuator based on a read signal of the servo information area by the head section and controlling disk access by the head section.
The control means also controls a position of the write head according to RW offsets set by the read data error recovering method according to a preferred embodiment of the present invention.
In addition, a disk device of another preferred embodiment of the present invention includes:
a sector-servo type disk recording medium where servo information is recorded beforehand in a servo area;
a head section accessing the disk recording medium;
a rotary actuator moving the head section along in a radial direction of the disk recording medium; and
a control means for controlling disk access by the head section based on a read signal of the servo information area by the head section.
The control means not only measures the amplitude of a read signal by the head section according to the read data error recovering method of a preferred embodiment of the present invention if a read data error of data recorded in the disk recording medium occurs, but also controls a position of the head section with the rotary actuator to execute error recovery procedure (ERP).